An image forming apparatus such as a multi-functional peripheral, a copy machine, or a printer is provided with a paper sheet cassette that houses paper sheets to be used for printing and performs paper feeding. Generally, paper sheet sizes placeable in the paper sheet cassette are regular sizes such as an A-type size and a letter size. Furthermore, in addition to the paper sheet cassette, a manual feed tray may be provided in the image forming apparatus. A paper sheet on the manual feed tray is replaced with another paper sheet, which then is brought to a state of being able to be fed. The manual feed tray, therefore, is advantageous in that changing to a paper sheet of a different size is easier compared with the paper sheet cassette. Furthermore, in a case where printing is performed by using a paper sheet of a size (a custom size) other than the regular sizes, the paper sheet is placed on the manual feed tray.
Patent Document 1 describes one example of such an image forming apparatus provided with a manual paper feed function. Specifically, Patent Document 1 describes an image forming apparatus that has the manual paper feed function, stores an image that should be formed, determines, based on the stored image and a set duplication magnification, a size of a recording paper sheet that should be fed manually, and informs a user of the thus determined size of the recording paper sheet. By this configuration, it is intended to inform a user of a size of a recording paper sheet that should be placed and thus to eliminate a burden on the user in an operation of placing a paper sheet (see Patent Document 1: claim 1 and paragraph [0004]).